Filtration is the heart of an aquarium, Fish needs to be crystal clear water to stay in an aquarium healthy. Filtration can be biological, mechanical and chemical. Product Features: The Filter Sponge Absorbs Dirt and clears the water. Suitable for both fresh and salt water. Fully submersible and ideal for any aquarium filtration. Completely Submersible And, be fit for fresh water and sea water. Super Quite, efficient energy economizing, easy to clean. The Sobo Slim Filter WP 308H is a heavy-duty external filtration system delivering powerful mechanical, chemical, and biological filtration, which produces crystal clear water in both fresh and marine aquariums.